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Abstract:

There is described a storage system and associated methods having
increased storage capacity for natural gas or methane. The systems and
methods store a larger quantity of natural gas at similar pressures and
volumes to conventional storage systems. The systems utilize readily
available carbons treated to increase the amount of natural gas adsorbed
to the carbon to store a high level of natural gas.

Claims:

1. A fuel storage system with increased storage capacity for natural gas
or methane storage comprising: a storage tank filled with activated
carbon; a means of regulating temperature of the carbon in the tank; flow
regulators; and particle detection system, wherein the particle detection
system is not an optical sensor system.

2. The fuel storage system of claim 1 wherein the temperature is lowered
or increased by internal coils.

3. The fuel storage system of claim 1 wherein the activated carbon
surface area is between about 1600 to about 3000 m2/g.

4. The fuel storage system of claim 3 wherein the activated carbon holds
greater than about 125 mg/gram of methane at a pressure at least 1500
psia.

5. The fuel storage system of claim 3 wherein the activated carbon holds
greater than about 225 mg/gram of methane at a pressure at least 3000
psia.

6. The fuel storage system of claim 3 wherein the activated carbon
increases the storage capacity for methane storage by about 150% at a
pressure at least 1500 psia.

7. The fuel storage system of claim 3 wherein the activated carbon
increases the storage capacity for methane storage by about 150% at a
pressure at least 3000 psia.

8. The fuel storage system of claim 1 wherein the activated carbon has a
particle size range between about 150 to about 400 mesh.

9. The fuel storage system of claim 1 wherein the temperature is
regulated via a control system to maintain a consistent flow of gas based
on the adsorption characteristics of the activated carbon.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of co-pending application U.S.
Ser. No. 12/134,290, filed Jun. 6, 2008, entitled Natural Gas Storage
Apparatus and Method of Use, which application is issued as U.S. Pat. No.
7,955,415 on Jun. 7, 2011. This application claims the benefit of U.S.
Provisional Application No. 60/942,239, filed Jun. 6, 2007. All of these
applications and the patent are incorporated herein by reference.

FIELD

[0002] The present disclosure relates to systems and associated methods
having increased storage capacity for natural gas or methane. In
particular, systems and methods utilizing carbon treated to increase the
amount of natural gas adsorbed to the carbon is disclosed. Thus, the
systems and methods store a larger quantity of natural gas at similar
pressures and volumes to conventional storage systems. Further the
production, shipping and utilization of the material in actual storage
tanks is described.

BACKGROUND

[0003] Activated carbon has the property of adsorbing hydrocarbon rich
gas, including methane or natural gas and allowing one to store more of
the gas in a tank of a given volume than the tank would hold in the
absence of carbon. However, there are problems involved in the handling
of carbon preventing successful commercial utilization of the process.
For example, carbon in the form of a fine powder or particles which may
catch fire when exposed to air and possible dust explosions present a
serious hazard. Also carbon in the form of a fine powder or particles
presents serious respiratory toxic risks upon inhalation. Additionally,
these forms of carbon have a tendency to be embedded and travel with the
gas when it is released. Carbon particles are known to clog valves and
equipment and are detrimental to equipment with moving parts. In the past
there is art wherein the carbons are formed into structured systems which
are placed into storage tanks. This potential solution increases the cost
of the carbon and the cost of the tank into which it is placed.

[0004] Various methods have been utilized to store and/or to increase the
storage capacity of tanks utilized for the storage of natural gas. U.S.
Pat. No. 5,458,258 discloses the use of hydroxy phenoxyether polymer
barrier liner for use in a tank storing compressed natural gas (CNG).
U.S. Pat. No. 5,603,360 describes the use of a flexible bladder for the
transportation of gas from a pipeline to a CNG automobile re-fueling
station. U.S. Pat. No. 5,676,180 further describes the use of this
bladder as a storage means for CNG at the automobile re-fueling station
or other end user locations. U.S. Pat. No. 6,217,626 discloses the use of
selected additives, which allows one to store the natural gas at
pressures around 1000 psia. For storage or pipeline transportation of
natural gas at pressures over 800 psia it was found advantageous to add
ammonia to the natural gas. U.S. Pat. No. 6,613,126 discloses a method of
separating natural gas into a high carbon component and a low carbon
component and using two tanks with adsorbent that will adsorb either the
high carbon or the low carbon fraction. They used activated carbon for
the absorption of natural gas, which required that normal paraffin be
pre-absorbed on the activated carbon prior to the absorption of natural
gas. This method requires the re-mixing of the components upon releasing
from the storage tanks and prior to use. The natural gas can not go into
the end use apparatus without this mixing step prior to utilization.

[0005] U.S. Pat. No. 4,999,330 discloses a process wherein bulk carbon is
reduced in bulk from about 50% to 200%, which gives an increase in
absorption capacity of about 50 to 200% in density. This process was
found useful in low pressure storage of CNG. This process also calls for
the use of a binder such as methyl cellulose.

[0006] Some activated carbons can increase the capacity of gas storage in
a tank. The gas molecules are held on the surface of the carbon (science
of surface chemistry) and thus the amount of gas that can be stored in a
tank increases based on the available carbon surface area. The economics
connected with such carbons makes them unattractive being sold at prices
ranging from US$50 to US$125 per pound. These materials do not solve the
problem at a financial cost that would allow the materials to be used in
increased mass storage of natural gas. Additionally these materials do
not allow for convenient filling and use of the methane or natural gas.

[0007] There was given in literature sources a carbon that appeared to
have the necessary gas adsorption characteristics; i.e., the carbon could
store twice or more the amount of natural gas in the same volume at the
same pressure, e.g. ambient temperatures at 3,000 psia, in the same size
tank. The carbon was identified as AX-21 and upon testing it was found
capable of storing 2.6 times the amount of methane in the same tank as
that tank without the presence of AX-21. This carbon is no longer
manufactured and if available the price was given as $50 a pound by the
manufacturer for purchases in large volume. The characteristics of this
particular carbon are given in Table 1.

[0008] Table 1 lists the samples and the "surface area" of the carbon
sample as measured by the adsorption of nitrogen in a specific test. The
results for surface area are available for many adsorbents from
commercial suppliers. However, nitrogen is not methane and, as the Table
shows, it was found that the correlation between the nitrogen capacity
and the methane capacity is very weak. Suitable carbons cannot be found
simply by selecting low density, high surface area carbons.

[0009] A carbon surface contaminated by undesirable adsorbates has limited
capacity for additional binding. Freshly prepared activated carbon
typically has a clean surface. Activated carbon production with heating
drives off potential adsorbates including water leading to a surface with
high adsorptive capacity. While activated carbon has been used in some
applications to remove selected hydrocarbons from water these
applications teach away from the use in this particular application as
water would interfere with the ability of the carbon to adsorb sufficient
gas to enable one to store about twice the quantity of gas within a
storage container. It is known that humidity is one of the factors that
influence the adsorptive properties of active carbon in air.

[0010] Accordingly, a method, device and/or system of a carbon material
stored, charged and discharged with gas having reduced risks of fire,
explosion and ability to stored at least twice the volume of gas as
normally stored is needed.

SUMMARY

[0011] The present disclosure describes a fuel storage system with
increased storage capacity for natural gas or methane storage. The fuel
storage system comprises a storage tank filled with activated carbon; a
means of regulating temperature; flow regulators; and a particle
detection system to detect carbon particle leaks. The regulation of
temperature is based on the instantaneous pressure in the system and the
flow rate at which the gas is removed is also described. This is
necessary to maintain the necessary flow of gas for use in energy
production such as automotive applications. In a further embodiment the
fuel storage tank is filled with zeolites or with metal-organic
frameworks.

[0012] There is further described a method of using this increased
capacity of a tank for storing natural gas or methane comprising filling
the tank with an activated carbon with selected adsorbent properties;
attaching a filter system to remove presence of particles; providing
means to remove stored gas from apparatus; and providing an optical
sensor feedback system.

[0013] There is also described a method of using this increased capacity
of a tank for storing natural gas or methane comprising filling the tank
with an adsorbent selected from the group consisting of zeolites and
metal-organic frameworks, attaching a filter system to remove presence of
particles; providing means to remove stored gas from apparatus; and
providing an optical sensor feedback system.

DEFINITIONS

[0014] The words "comprising," "having," "containing," and "including,"
and other forms thereof, are intended to be equivalent in meaning and be
open ended in that an item or items following any one of these words is
not meant to be an exhaustive listing of such item or items, or meant to
be limited to only the listed item or items

[0015] The term `zeolites` refer to hydrated aluminosilicate minerals
having a micro-porous structure and includes both natural and synthetic
types.

[0016] The term `metal-organic frameworks` refer to crystalline compounds
consisting of metal ions or clusters coordinated to often rigid organic
molecules to form one-, two-, or three-dimensional structures that can be
porous.

[0017] The term `natural gas` refers to gas produced from petroleum wells
or by anaerobic digestion of organic material whose composition is
predominantly methane, CH4, but which can contain other
hydrocarbons.

[0018] The term `activated carbon` refers to a form of carbon having very
fine pores: used chiefly for adsorbing gases or solutes, as in various
filter systems for purification, deodorization, and decolorization.

[0019] The term `tank` refers to a receptacle, container, or structure for
holding a liquid or a gas.

[0020] The following abbreviations are used:

[0021] psia pressure in pounds per square inch atmospheric

[0022] BET Brunauer-Emmett-Teller (BET) theory

[0023] CNG Compressed natural gas

[0024] MOFs Metal-Organic Frameworks

[0025] All publications, including patents, published patent applications,
scientific or trade publications and the like, cited in this
specification are hereby incorporated herein in their entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The foregoing aspects and advantages of present disclosure will
become more readily apparent and understood with reference to the
following detailed description, when taken in conjunction with the
accompanying drawings, wherein:

[0027] FIG. 1 illustrates a block diagram of a storage tank system.

[0028] The FIGURE is diagrammatic and is not drawn to scale. Corresponding
parts generally bear the same reference numerals.

DETAILED DESCRIPTION

Fuel Storage System

[0029] A fuel storage system with increased storage capacity of natural
gas or methane is disclosed.

[0030] Referring to FIG. 1, the block diagram illustrates the features of
an exemplary fuel storage system which is designed to increase the
capacity of a tank wherein natural gas or methane is stored.

[0031] The fuel storage system comprises a tank 3, a valve with a
supported membrane or filter 6, a dual stage regulator 10 & 14, a powered
solenoid valve 17 (normally closed), a temperature controller 18 and
optionally a flow/particle sensor 16. The tank is of sufficient size to
hold the desired volume of gas to be stored at various pressures ranging
from atmospheric to about 4,000 psia at ambient temperature.

[0032] To increase the amount of methane stored in the tank 3 of the fuel
storage system, the tank 3 is filled with activated carbon. The natural
gas or methane is adsorbed to the surface area of the carbon. In another
embodiment the tank 3 is filled with an adsorbent selected from the group
consisting of metal-organic frameworks and zeolites.

[0033] Temperature effects on adsorption and desorption are large, and
measurements are usually conducted at a constant temperature. The lower
the temperature the great the adsorption capacity. Isotherms are used to
predict the effect of temperature changes. The degree of heat generation
can not be predicted and is based on properties such as (a) gas flow
rate, (b) water vapor, and (c) presence of reactive type compounds such
as ketones, aldehydes that may be present as impurities. Typically
empirical relationships are needed to match the flow rate desired with
the current pressure, temperature and type of specific carbon in the
tank.

[0034] A valve fitting with a supported membrane 6 or a fine filter, e.g.,
0.1 to 0.5 micrometer pore size is installed between the regulator 12 and
the tank. Further the supported membrane filter 6 may be contained within
the tank. The membrane or filter 6 is supported on both sides with mesh
to allow both the high pressure filling of the tank and the higher
pressure relief of the tank that allows the natural gas to pass out of
the tank. The threading of the membrane/filter system is such that it
allows either a single or dual stage regulator. The dual stage regulator
permits one to remove natural gas from the system while ensuring that
carbon is not entrained in the gas stream if there is a membrane rupture.
Dual stage regulators also allow for a wide disparity between the storage
pressure and the use pressure of gases in a tank. Optionally an optical
particle detection system could be installed in the line outside the
tank. The particle detection system 7, 8, is connected to a solenoid
prior to the regulator to shut down the system in the event of a
filter/membrane rupture. The tank may be wound with a coil or shell
either internally or externally that are used to provide heat to the
tank. The diagram in FIG. 1 illustrates a tank with a jacket for the
heating and cooling processes. There are other sensors that can be used
to regulate the tank parameters and flow that are known to one of
ordinary skills in the art.

The Method

[0035] An inexpensive activated carbon is selected by testing the
absorption characteristics of the carbon using methane or natural gas.
This testing is conducted at pressures of at least about 1,500 psia.
Carbons that can hold at least 30% more methane or natural gas than an
equivalent volume of a tank at the same temperature and pressure are
considered for further treatment to increase their ability to adsorb.
Carbons that can hold at least 75 percent more methane or natural gas in
a given volume than can be held in an equivalent tank volume without the
presence of carbon at the same pressure and temperature are useful
adsorbents to increase the mass of natural gas within a tank. A further
selection of these carbons is based on their particle size which should
be a size that is easily conveyed pneumatically in a stream of an inert
gas; for example, nitrogen. In exemplary implementations, a particle size
range of between about 150 to about 400 mesh is useful.

[0036] These carbons are very flammable and thus they are normally stored
wet to reduce the danger of fire or explosion during handling and
shipping. Prior to be placing in a tank the carbons are dried in an oven
or air heating and drying system at 110° C. with or without a
vacuum and immediately conveyed into storage tanks. Preferably the
transfer of the carbon is pneumatically in an inert gas atmosphere.

[0037] Zeolites, MOFs, and carbon are all considered toxic hazardous
materials for respiratory inhalation. It is critical to keep these
materials contained within the system.

[0038] After the storage tank is filled under a minimal pressure (for
example about 30 psia) with the carrier gas, the tank is allowed to
equilibrate at atmospheric pressure. A special valve fitting is installed
with a supported membrane or fine filter between the tank itself and the
regulator. In exemplary implementations, the pore size of the filter in
between about 0.1 and 0.3 micrometers. In one aspect, the membrane or
filter is supported on both sides with mesh to allow both high pressure
filling of the tank and higher pressure relief of the tank to allow the
natural gas to pass out of the tank.

[0039] The filter/membrane system is threaded such that both the filling
and removal of the gaseous material can be accommodated by single or dual
stage regulators. In one embodiment dual stage regulators are utilized
when removing natural gas from the tank to ensure that carbon is not
entrained in the gas stream if there is a membrane rupture. Optionally an
optical particle detection system can be installed in the line outside
tank prior to engine intake of the filter/membrane system connected to a
solenoid prior to the regulator to shut down the system in the event of a
filter/membrane failure. The optical particle detection system is based
on light scattered from any particles that may break though the barrier.
The scattered light is detected at an angle from the illuminating light
source (e.g. an LED) that is active when the tank is being discharged.
The angle of observation is matched to maximize the signal based on
classical electromagnetic theory. Typically the light scattered at
90° to 135° from the incident radiation is used.

[0040] The absorption characteristics of most carbons or other adsorbents
that are useful for this process are not linear for the removal and
introduction of the gaseous material for storage. This is particularly a
problem in the removal of natural gas or methane at low pressure near the
depletion of the gas in the tank. In some applications, for example in a
vehicle, the storage tanks can be wound with a coil or shell either
external or internal to the actual tank which allows fluid from the
vehicle manifold or radiator system to heat the storage tank. As an
example if the tanks operate in the range of 3,000 to 3,600 psia, a
pressure sensor tied to a solenoid would allow heating to occur when the
pressure in the tank drops to 1,000 psia or other suitable pressure. The
pressure sensor can also be coupled with a temperature sensor as the
removal of the natural gas is also influenced by the temperature. The
temperature and pressure setting is automatically adjusted for the
environment/outside temperature by using the temperature ratio as the
trigger to open the solenoid. For rapid heavy loads the escape of gas
alone will cool the tank and may cause difficulties in further removal of
the gas. A thermal system that works on the ratio of the tank temperature
to the ambient temperature alleviates this problem.

[0041] As described above and herein there are several useful sensor
feedback systems that may be optionally used with the method of natural
gas or methane storage system. These useful sensor feedback systems are:

[0042] A particle detector sensor 7, 8, 9 which closes the solenoid
regulating the release of the gas from the tank.

[0043] A pressure sensor 15 which opens a heating system when the pressure
of the gas within the tank is low.

[0044] A temperature sensor 4 to assist in controlling the pressure
setting in cold weather or when there are periods of rapid gas removal
from the storage tank.

[0045] The Method comprises the following basic steps: [0046] 1) Use of
an activated carbon with selected adsorbent properties for natural gas or
methane storage within a tank. [0047] 2) Attaching a filter/membrane
system to remove entrained carbon from gas stream. [0048] 3) Providing
means to remove stored gas from system. [0049] 4) Providing sensors and
feedback systems that allow for safe operation of the unit, with flow
characteristics over varying pressures related to the desired removal
rate form the tank.

[0050] In another embodiment the Method comprises the following basic
steps: [0051] 5) Use of an adsorbent selected from the group consisting
of zeolites and metal-organic frameworks for natural gas or methane
storage within a tank. [0052] 6) Attaching a filter/membrane system to
remove entrained adsorbent from gas stream. [0053] 7) Providing means to
remove stored gas from system. [0054] 8) Providing sensors and feedback
systems that allow for safe operation of the unit, with flow
characteristics over varying pressures related to the desired removal
rate form the tank.

[0055] The system as described herein provides a method of storing natural
gas or methane wherein a larger quantity of natural gas or methane can be
contained within a tank of a given volume at the same pressure than the
tank would hold without utilizing activated carbon.

[0056] This method can be used with all, selected or none of the sensor
feedback systems

Selecting Activated Carbon

[0057] The absorption characteristics of activated carbon are tested as in
Example A. Carbons that can hold at least 30% more methane or natural gas
than the amount of methane without carbon held in the same volume of tank
at the same temperature and pressure are considered for treatment to
increase their adsorbent characteristics.

Improving Carbon Capacity

[0058] Activation of carbon is normally performed by pyrolysis or
subsequent oxidation by an agent such as steam at temperatures up to
950° C. To reactivate carbons or to further activate carbons, a
simple oxidation system based on the use of hydrogen peroxide under high
pressure and temperature has been used. Normally the hydrogen peroxide
solution (3-10%) is placed with the carbon particles in high pressure (up
to 2,000 psia) at temperatures up to 400° C. for periods up to
several hours. A typical treatment parameters is about 300° C. to
350° C. at 1700 psia for two (2) hours. The degree of the reaction
is dependent on the specific carbon and can only be determined by
measurement against methane or natural gas absorption. An alternative
system for some carbons is to heat the carbon in a flowing stream of
inert gas such as helium at 300° C. to 400° C. to remove
hydrocarbons and impurities in the carbons. Different carbons from
different sources respond differently to the oxidation or the inter gas
method. The purpose of such treatment is to increase the adsorption sites
for methane or natural gas in the structure of the carbon thus increasing
the space for binding.

[0059] Under some conditions the structure of the carbon will hold
multilayers of the natural gas or methane on the carbon structure.
Typically the storage of more than one layer of gas is described by a
relationship discovered by Brunauer, Emmett and Teller and known as the
BET Adsorption Isotherm (Physical Chemistry, Gucker & Seifert, pgs.
652-661, 1966 (WW Norton & Co, NY)). The objective of treatment is to
increase the number of layers of gas that can be held in the carbon
structure.

Example A

Measurement of Activity

[0060] To measure the effectiveness of a specific carbon sample, a 352 ml
container was used which was built to withstand pressures of at least
1,500 psia. The container is weighed (wt. I), filled with methane at the
selected pressure, for example, 1,500 psia, and reweighed (wt. II). The
first weight (wt. I) is subtracted from the second weight (wt. II) to
obtain the weight of methane (wt. NC) the container holds at a selected
pressure, for example, 1500 psia, and ambient temperature.

[0061] The container is emptied and filled with the carbon and weighed
(wt. III) at room temperature and the selected pressure. Methane is again
introduced into the container which contains the carbon previously
weighed. The container with carbon and methane at the selected pressure
and ambient temperature is reweighed (wt. IV). Subtracting the weight of
the container plus carbon (wt III) from the weight of the container,
carbon and methane (wt. IV) gives the weight of the methane held within
the container (wt. C).

[0062] The weight of methane (wt. NC) in the container without carbon
present from the measured weight of methane (wt. C) to measure the weight
of methane adsorb onto the carbon; i.e., the increase in the amount of
methane that can be held within the container at a set pressure and
temperature.

[0063] The table given below, Table 1, details some of the results from
various carbons. The last three carbons are considered acceptable for the
process as described.

[0064] The first column in the Table 1 lists the sample; the second column
is the "surface area" of the carbon as measured by the adsorption of
nitrogen in a specific test. The results for BET surface area are
available for many adsorbents from commercial suppliers. The term BET is
an acronym for the Brunauer-Emmett-Teller (BET) theory which is a
standard means to calculate the surface area from the weight gain of the
adsorbent exposed to nitrogen gas.

[0065] However, nitrogen is not the same as methane and, as the Table
shows, the correlation between the nitrogen capacity and the methane
capacity is very weak. While it is better to start with the higher
surface area carbons with lower density (to keep the weight in the tanks
lower) there is no certainty that one can find suitable carbons simply by
selecting low density, high surface area carbons.

[0066] It appears that the last four carbons in Table 1 could be suitable
for further study if they were available economically. Of these the last
two are not commercially viable as they are too expensive for commercial
use and the last one (AX-21) is no longer available. Activated carbons
utilized to increase the storage capacity of natural gas or methane have
a surface area between about 1600 to about 3000 m2/g to methane (not
nitrogen). They conform to the BET description and temperature can be
used to regulate the desorption isotherms. In other implementations, the
activated carbon adsorbing greater than about 225 mg/gram of methane
increases the storage capacity of a fuel tank.

[0067] While the above description contains many particulars, these should
not be considered limitations on the scope of the disclosure, but rather
a demonstration of embodiments thereof. The apparatus and methods
disclosed herein include any combination of the different species or
embodiments disclosed. Accordingly, it is not intended that the scope of
the disclosure in any way be limited by the above description. The
various elements of the claims and claims themselves may be combined in
any combination, in accordance with the teachings of the present
disclosure, which includes the claims.